I think the concept is new to him. I'm not sure how knowledgeable or adventurous he might be, but here is the thread where I volunteered your expertise as a consultant.

Ok, thanks for that clarification. Just now I knocked up an "Open PDF externally" plugin, but while doing so it gave me a better idea. Instead I am writing an "Open format externally" plugin, where you can configure it for EPUB, PDF or any other format you like rather than having all individual plugins for each format. Just in case in future someone says they want a LIT or MOBI or whatever format supported, they can just add it themselves to a tweak setting. Will post it here when done.